The present invention relates to a rolling bearing provided with a sealing member for preventing the leakage of enclosed grease as well as the entrance of dust, water, muddy water, etc. into the interior of the bearing as in wheel rolling bearing for bearing the wheel of automobile or railway vehicle or rolling bearing for steel rolling device.
For example, a wheel rolling bearing for bearing the wheel of automobile is occasionally forced to be not only exposed to much dust but also operated while the wheel being dipped in muddy water. The rolling bearing is also exposed to wash water when the automobile is washed. Due to outdoor use, a rolling bearing for bearing the wheel of railway vehicle is also exposed to dust and weather in operation and to wash water when the vehicle is washed.
When the rolling bearing is used under such severe conditions, the sealing member of the rolling bearing is subject to removal of lubricant such as grease which has been previously applied to a lip portion of the sealing member. Thus, an elastic member constituting the lip portion undergoes abnormal abrasion that deteriorates the sealing properties of the sealing member, thereby making it more likely that water, dust, etc. can enter into the interior of the rolling bearing. As a result, the rolling bearing can difficultly maintain its desired properties over an extended period of time. In the worst case, the rolling bearing can break in an early stage. Even if the rolling bearing can maintain its desired sealing properties, the heat generated by sliding of the lip portion with respect to the bearing member causes the deterioration of lubricant such as enclosed grease because the lip portion possibly has no sufficient lubricant present thereon. In this case, it is difficult to maintain desired properties over an extended period of time.
Further, the rolling bearing for steel rolling device is much exposed to dust such as iron ore dust and coke dust and also is used while being sprayed with cooling water for cooling the bearing itself. Accordingly, the rolling bearing for steel rolling device is difficult to maintain its desired properties over an extended period of time similarly to the rolling bearing for vehicle.
Heretofore, the sealing member of the foregoing wheel rolling bearing has comprised an elastic member formed by a rubber material composition having proper additives incorporated in an ordinary nitrile rubber. As well known, a rolling bearing for automobile wheel is used outdoor and thus can be exposed to much dust. The rolling bearing is also used under conditions such that it is exposed to rain water or wash water or, in the worst case, dipped in muddy water. A sealing member comprising an elastic member formed by an ordinary nitrile rubber material composition exhibits sufficient sealing properties even while being lubricated under so-called clean conditions such that it is relatively little subject to exposure to water and dust. However, under recent requirements that the life of wheel bearing be prolonged or the torque of the wheel bearing be lowered to enhance the fuel economy of automobile, the grease applied to the lip portion can undergo softening or emulsification in an extreme case under the foregoing severe conditions. When the grease runs out, it is impossible to maintain desired lubricity sufficiently. Further, the lip can undergo abnormal abrasion that deteriorates the sealing properties of the sealing member, so that it is more likely occurred that dust or water can enter into the interior of the bearing and hence making it impossible to maintain desired bearing properties over an extended period of time. In order to improve the sealing properties of the sealing member, the increase of the fastening margin can be proposed. However, this approach causes the rise of torque, so that the lip likely undergo abrasion that deteriorates the sealing properties of the sealing member. Further, the resulting abrasion heat causes the deterioration of grease so that the life of the bearing is likely reduced.
In an attempt to eliminate these defectives, it has been practiced to incorporate a solid lubricant such as fluororesin and molybdenum disulfide and a wax such as paraffin wax and aliphatic acid amide in the rubber composition constituting the elastic member so that the abrasion of the lip portion can be inhibited and the generation of heat due to sliding and the rotary torque can be lowered even when the grease runs out, making it impossible to keep the bearing lubricated sufficiently.
Further, the wheel rolling bearing provided with a sealing member comprising an elastic member formed by the conventional nitrile rubber composition cannot operate for a sufficiently prolonged life under the foregoing severe working conditions.
It is therefore an object of the present invention to provide a rolling bearing having a prolonged life suitable for wheel, railway vehicle and steel rolling mill comprising a sealing member which exhibits fair sealing properties even under such severe conditions.
The foregoing object of the present invention will become apparent from the following detailed description and examples.
The object of the invention is accomplished with a rolling bearing comprising an outer ring having an outer raceway formed on the inner surface thereof, an inner ring having an inner raceway formed on the outer surface thereof, a plurality of rolling elements rollably provided between the outer ring and the inner ring, and a sealing member for sealing an axial opening of a space defined between the inner surface of the outer ring and the outer surface of the inner ring in which the rolling elements are provided, wherein the sealing member is formed by an elastic member made of a vulcanizable rubber composition obtained by blending a carboxylated acrylonitrile-butadiene rubber with at least carbon black.
Further, in addition to above the construction, the carboxylated acrylonitrile-butadiene rubber may further comprises a silicone oil incorporated therein.